Spin qubits in graphene quantum dots

Trauzettel, Björn; Bulaev, D. V.; Loss, Daniel; Burkard, Guido

doi:10.1038/nphys544

Cited by 1,024 publications

(1,017 citation statements)

References 33 publications

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“…However, spin lifetimes measured in SLG spin valves are much shorter (0.05 -1.2 ns) 6-9 than predicted (100 ns -1 s) [1][2][3][4][5] . Thus, the origin of spin relaxation in SLG has become a central issue for graphene spintronics and has motivated intense theoretical and experimental studies.…”

Section: Introductionmentioning

confidence: 81%

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Spin Relaxation in Single-Layer Graphene with Tunable Mobility

et al. 2012

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Abstract:Graphene is an attractive material for spintronics due to theoretical predictions of long spin lifetimes arising from low spin-orbit and hyperfine couplings. In experiments, however, spin lifetimes in single layer graphene (SLG) measured via Hanle effects are much shorter than expected theoretically. Thus, the origin of spin relaxation in SLG is a major issue for graphene spintronics. Despite extensive theoretical and experimental work addressing this question, there is still little clarity on the microscopic origin of spin relaxation. By using organic ligand-bound nanoparticles as charge reservoirs to tune mobility between 2700 and 12000 cm 2 /Vs, we successfully isolate the effect of charged impurity scattering on spin relaxation in SLG. Our results demonstrate that while charged impurities can greatly affect mobility, the spin lifetimes are not affected by charged impurity scattering. Keywords:graphene; spintronics; spin relaxation; mobility; charged impurity scattering 2 Single layer graphene (SLG) is a promising material for spintronics due to theoretical predictions of long spin lifetimes based on its low intrinsic spin-orbit and hyperfine couplings [1][2][3][4][5] . However, spin lifetimes measured in SLG spin valves are much shorter (0.05 -1.2 ns) 6-9 than predicted (100 ns -1 s) [1][2][3][4][5] . Thus, the origin of spin relaxation in SLG has become a central issue for graphene spintronics and has motivated intense theoretical and experimental studies. Theoretical studies of spin relaxation include impurity scattering 10 , ripples 5 , spin orbit domains 11,12 , and substrate effects 13 , while experimental studies have investigated contact-induced spin relaxation 7, 9, 14 , ripples 15 , band structure effects 6,14,16 , edge effects 7 and charged impurity scattering 6, 8 .However, apart from recognizing the requirement for high quality tunneling contacts to suppress contact-induced spin relaxation 9 , there is little clarity regarding the origin of spin relaxation. To address the situation, it is crucial to develop experimental techniques that systematically isolate the various microscopic sources of spin relaxation.In this work, we successfully isolate the effect of charged impurity scattering on spin relaxation in SLG by exploiting the novel tunable mobility imparted by organic ligand-bound nanoparticles on the SLG surface 17 . The nanoparticles act as charge reservoirs that freely transfer charge with graphene at room temperature. At low temperature, the frozen charge distribution on the nanoparticles results in SLG mobility ranging from 2700 to 12000 cm 2 /Vs. This approach is able to isolate the effect of charged impurity scattering on spin relaxation more clearly than previous investigations based on adatom deposition 8 . This is because depositing adatoms to the graphene surface could introduce additional effects such as short-range scattering, lattice deformation, and/or spin-orbit coupling, whereas such effects should be minimized in the current approach. Additionally, we utilize tunne...

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Section: Introductionmentioning

confidence: 81%

“…Single layer graphene (SLG) is a promising material for spintronics due to theoretical predictions of long spin lifetimes based on its low intrinsic spin-orbit and hyperfine couplings [1][2][3][4][5] . However, spin lifetimes measured in SLG spin valves are much shorter (0.05 -1.2 ns) 6-9 than predicted (100 ns -1 s) [1][2][3][4][5] .…”

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confidence: 99%

Spin Relaxation in Single-Layer Graphene with Tunable Mobility

et al. 2012

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“…The obtained constant level spacing of 1.75 meV over a wide energy range is in good agreement with the expected single-particle energy spacing in bilayer graphene quantum dots. Finally, we investigate the evolution of the electronic excited states in a parallel magnetic field.Keywords: graphene, bilayer graphene, quantum dot, double quantum dot, excited states Graphene quantum dots (QDs) are interesting candidates for spin qubits with long coherence times [1]. The suppressed hyperfine interaction and weak spin-orbit coupling [2, 3] make graphene and flat carbon structures in general, promising for future quantum information technology [4].…”

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confidence: 99%

Electronic Excited States in Bilayer Graphene Double Quantum Dots

et al. 2011

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We report tunneling spectroscopy experiments on a bilayer graphene double quantum dot device that can be tuned by all-graphene lateral gates. The diameter of the two quantum dots are around 50 nm and the constrictions acting as tunneling barriers are 30 nm in width. The double quantum dot features addition energies on the order of 20 meV. Charge stability diagrams allow us to study the tunable interdot coupling energy as well as the spectrum of the electronic excited states on a number of individual triple points over a large energy range. The obtained constant level spacing of 1.75 meV over a wide energy range is in good agreement with the expected single-particle energy spacing in bilayer graphene quantum dots. Finally, we investigate the evolution of the electronic excited states in a parallel magnetic field.Keywords: graphene, bilayer graphene, quantum dot, double quantum dot, excited states Graphene quantum dots (QDs) are interesting candidates for spin qubits with long coherence times [1]. The suppressed hyperfine interaction and weak spin-orbit coupling [2, 3] make graphene and flat carbon structures in general, promising for future quantum information technology [4]. Significant progress has been made recently in the fabrication and understanding of graphene quantum devices. A "paper-cutting" technique enables the fabrication of graphene nanoribbons [5][6][7][8][9][10][11][12][13], quantum dots [14][15][16][17][18][19], and double quantum dot devices [20][21][22][23], where a disorder-induced energy gap allows confinement of individual carriers in graphene. These devices allowed the experimental investigation of excited states [16,21], spin states [19] and the electron-hole crossover [17]. However, all of these studies were based on single-layer graphene and showed a number of device limitations related to the presence of disorder, vibrational excitations and to the fact that the missing band gap makes it difficult to realize soft confinement potentials and "well-behaving" tunneling barriers. In particular, it has been shown that intrinsic ripples and corrugations in single-layer graphene can lead to unintended vibrational degrees of freedom [24] and to a coherent electron-vibron coupling in graphene QDs [25]. Bilayer graphene is a promising candidate to overcome some of these limitations. In particular it allows to open a band gap by an out-of-plane electric field [26][27][28], which may enable a soft confinement potential and may reduce the influence of localized edge states. More importantly, it has been shown that ripples and substrate-induced disorder are reduced in bilayer graphene [29], which increases the mechanical stability and suppresses unwanted vibrational modes.Here, we present a bilayer graphene double quantum dot (DQD) device, with a number of lateral gates. These local gates allow to tune transport from hole to electron dominated regimes and they enable to access different device configurations. We focus on the DQD configuration and show characteristic honeycomb-like charge stability dia...

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“…Promising results for the spin-polarized current lifetimes in carbon nanotubes [6,7,8] and graphene [9] unambiguously confirm the potential of these materials. A number of quantum dot devices, components of solid-state quantum computers, based on carbon nanostructures have been proposed recently [10,11,12,13]. Hyperfine interactions (HFIs), the weak magnetic interactions between the spins of electrons and nuclei, become increasingly important on the nanoscale.…”

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confidence: 99%

Hyperfine Interactions in Graphene and Related Carbon Nanostructures

2008

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Hyperfine interactions, magnetic interactions between the spins of electrons and nuclei, in graphene and related carbon nanostructures are studied. By using a combination of accurate first principles calculations on graphene fragments and statistical analysis, I show that both isotropic and dipolar hyperfine interactions can be accurately described in terms of the local electron spin distribution and atomic structure. A complete set of parameters describing the hyperfine interactions of 13 C and other nuclear spins at substitution impurities and edge terminations is determined.PACS numbers: 71.70. Jp, 81.05.Uw, 03.67.Pp Graphene and related carbon nanostructures are considered as potential building blocks of future electronics, including spintronics [1] and quantum information processing based on electron spins [2] or nuclear spins [3]. Carbon nanostructures are attractive for these applications because of the weak spin-orbit interaction in materials made of light elements [4,5]. Promising results for the spin-polarized current lifetimes in carbon nanotubes [6,7,8] and graphene [9] unambiguously confirm the potential of these materials. A number of quantum dot devices, components of solid-state quantum computers, based on carbon nanostructures have been proposed recently [10,11,12,13]. Hyperfine interactions (HFIs), the weak magnetic interactions between the spins of electrons and nuclei, become increasingly important on the nanoscale. In carbon nanostructures the interactions of electron spins with an ensemble of nuclear spins are expected to be the leading contribution to the electron spin decoherence [4,7,14]. Minimizing HFIs is thus necessary for achieving longer electron spin coherence times [15]. In some other instances the HFIs play an important role as a link between the spins of electrons and nuclei in the nanostructures [3,16,17,18] underlying the implementations of quantum information processing involving nuclear spins. Probing HFIs with magnetic resonance techniques also provides a wealth of information about structure and dynamics of carbon materials [19]. A common understanding and an ability to control the HFIs are thus necessary for engineering future electronic devices based on graphene and related nanostructures.In this Letter, I study the hyperfine interactions in carbon nanostructures by using a combination of accurate first principles calculations on graphene fragments and statistical analysis. I show that the interaction of the conduction (low-energy) π electron spins with nuclear spins can be described in terms of only the local (on-site and first-nearest-neighbor) π electron spin distribution and the local atomic structure. The conduction electron spin distribution can be determined using simpler computational approaches (e.g. tight binding or analytical approximations [20,21]) and tuned by tailoring nanos- FIG. 1: (Color online). Projections of the spin-polarized conduction electron density ρ s c (r) (a) and the total spin density ρ s (r) (b) on the plane of an electron-doped graphene...

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Spin qubits in graphene quantum dots

Cited by 1,024 publications

References 33 publications

Spin Relaxation in Single-Layer Graphene with Tunable Mobility

Spin Relaxation in Single-Layer Graphene with Tunable Mobility

Electronic Excited States in Bilayer Graphene Double Quantum Dots

Hyperfine Interactions in Graphene and Related Carbon Nanostructures

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